Loud-speaking communication system



Oct. 11, 1949. p, DEMERS 2,484,691

LOUDSPEAKING COMMUNICATION SYSTEM Filed Feb. 14, 1946 IIN VE/V TOR P e DEMERS ATTORNEY Patented Oct. 11, 1949 LOUD-SPEAKING COMMUNICATION SYSTEM Paul E. Demers, Montreal, Quebec, Canada, assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application February 14, 1946, Serial N0. @595 11 Claims. 1

This invention relates to intercommunicatlon systems and particularly to two-way ofllce intercommunication systems of the loudspeaking type.

Each station of a communication system of the above-indicated type is equipped with closely associated speech transmitting microphones and loudspeaking receivers and due to the acoustic coupling of such speech input and output devices, serious limitations have been imposed on the overall efficiency of such systems. Various methods of reducing the effects of acoustic coupling have been devised in the past and usually have involved complex circuit arrangements and highly sensitive controls which necessarily increase the initial and maintenance costs of such systems and in many cases render the cost prohibitive. One of the common methods resorted to involves the use of a talk-listen" key which imposes upon the user the objectionable task of operating a key to one position during the speech transmitting period and re-operating the key to another position during the speech receiving period.

It is the object of this invention to provide a simple, inexpensive and eflicient loudspeaking communication system in which the effects of acoustic coupling are entirely eliminated without imposing on the user any requirements other than those incidental to the normal activation of the microphone by speech signals.

It is well known that ordinary speech contains all frequencies from 100 cycles up, and that better than 90 per cent articulation can be obtained with speech if all frequencies above 400 cycles are utilized for speech purposes. In other words, all speech frequencies below 400 cycles may be eliminated from the speech frequency band without noticeably afiecting the quality of reproduction.

In accordance with a feature of this invention those frequencies of speech which are not essential to substantially perfect articulation are eliminated from the speech frequency band during speech transmission and are utilized to control the speech transmitting and receiving channels in such a manner that the transmitting channel is automatically rendered effective, under control of the eliminated frequencies, to transmit the remaining frequencies of the speech band, and the receiving channel is simultaneously disabled.

A further feature of the invention contemplates the provision of a signaling means at each station of the communication system which responds to the activation of the transmitting microphone at another station to visually indicate such occurrence.

These and other features of the invention will be best understood from the following description when read in connection with the accompanying drawing which shows a two-way loudspeaking oflice intercommunicating system embodying the features of the invention.

The system disclosed in the drawing, by way of illustration, shows two stations A and B of an intercommunication system each of which is equipped with a microphone I0 and a loudspeaking receiver I2 which respectively terminate the speech transmitting and receiving channels I3 and I4 at their respective stations. The remaining equipment for each station comprises a oneway amplifier I5, a dividing network I6, a fullwave copper oxide rectifier I1 and a fast operating, slow releasing relay I8. A lamp signal I! may be located at each station. I

The microphones I0, loudspeakers I2 and amplifiers I5 may be of any well-known designs. The dividing network consists of an inductance coil 20 and a condenser 2| serially connected together and bridged across the -output of the amplifier I5. This dividing .network is subjected to the frequencies of the speech signals impressed on the microphone I0 and amplified by amplifier I 5, and functions as a means for separating these frequencies into two subbands of frequencies, one subband including those frequencies of the speech band above 400 cycles and the other subband including those frequencies of the speech band below 400 cycles. The frequencies above 400 cycles appear in the coil 20 whereas the frequencies be low 400 cycles are derived across the terminals of the condenser 2|. The input terminals of fullwave rectifier I! are connected to the terminals of condenser 2| so that the rectifier is subjected to, and rectifies only currents of the frequencies below 400 cycles. The relay I8 is connected to the output terminals of rectifier I1 and therefore responds selectively to the subband of frequencies below 400 cycles.

Relay I8 at its two upper armatures and front contacts controls the connection of the outgoing speech transmitting channel at each station to the coil 20 of the corresponding dividing network. At its first and second lower armatures and front contacts relay I8 of each station controls the speech receiving channel I4 of the corresponding station, it being observed that, with the relays I8 in their normal unoperated condition the speech channel I3 of station A is disconnected from the speech receiving channel I 4 at station B and similarly, the speech channel I3 of station B is disconnected from the receiving channel It at station A. When operated, relays I8 effect the the dividing network I6. The dividing network functions to separate the speech frequency band into two subbands, one subband containing frequencies above 400 cycles appearing at the terminals of coil 20 and the other subband containing frequencies below 400 cycles appearing at the terminals of condenser 2|.

The current of the lower frequency band is rectified at IT and traverses the winding of relay I8 as rectified current to which current the relay responds. Relay I8 accordingly operates quickly :and at its two upper armatures and front contacts connects the speech channel, or line c to the output terminals of coil 20, and at its first and second lower armatures and front contacts disconnects the loudspeaker I2 from the speech channel, or line D. Speech channels, or lines C and D constitute connecting links between the stations A and B. Thus the subband of frequencies containing those frequencies above 400 cycles and which furnish substantially perfect speech articulation are projected over channel C to be reproduced by the loudspeaker I2 at station B, it being observed that channel D is connected through to channel It and the loudspeaker I2 by the first and second lower armatures and back contacts of relay I8 at station 13. Thus those frequencies above 400 cycles which are impressed on the microphone Ill at station A are reproduced by the loudspeaker I2 at station 3.

It will now be observed that since only those frequencies above 400 cycles are reproduced by the loudspeaker I2 at station B, their impinging on the microphone ill at station B will be ineffectual to disturb the speech paths between the stations since relay I8 at station B responds to frequencies only below 400 cycles. The effects of acoustic coupling are therefore eliminated since the acoustic energy from the loudspeaker does not contain the frequency components required to operate the relay.

It will be observed further that should the parties at stations A and B attempt to talk simultaneously, a condition of silence would prevail since, under this condition, both relays I8 would be operated. To insure against the simultaneous talking of both parties, a lamp signal I8 may be provided at each station so as to be lighted when the relay at the other station is operated. Thus when relay I8 of station A is operated the third lower armature and front .contact thereof complete an energizing circuit for lamp I9 at station B. Lamp I9 is lighted in this circuit to visually indicate to the party at station B that he should not talk at this time but should wait until the lamp I9 is extinguished marking the cessation of speech at station A and the consequent deenergization of relay I8 thereat. The lamp I8 at station A is similarly controlled by relay I8 of station B and serves a similar purpose. The purpose of the network 25 is to introduce a loss in the local speaker sufficient to prevent acoustic feedback but leaving an adequate level to hear the speech when both parties happen to talk at 7 the same time and when relay I8 is not equipped to open the circuit to the local speaker.

It'is apparent from the foregoing description that only those frequencies of the speech band which are necessary to the production of substan- 4 tially perfect speech articulation are utilized for speech transmission, and those frequencies which are not essential to good speech articulation are eliminated from the speech and are employed to 7 control the completion and disabling of the transmitting and receiving paths respectively, at each station.

No attempt has been made to illustrate station selecting or signaling means nor has any attempt been made to expand the disclosure to illustrate the application of this invention to conferenceconnections. The disclosure illustrates the fundamental concept of the invention and further elaiboration to include station selection and conference facilities is not necessary to a complete understanding of the invention.

What is claimed is: 1. In a loudspeaking intercommunicating system, a first station, a second station, a normally discontinuous line extending between said stations, a speech transmitter at said first station, means at said first station for dividing the frcquency band of speech signals impressed on said transmitter into two subbands, and means selectively responsive to the frequencies of one ,subband for rendering said line continuous and for projecting the other subband of frequencies thereover.

2. In a loudspeaking intercommunicating system, a first station, a second station, a pair of normally discontinuous lines extending between said stations each transmitting at one station in a speech transmitting device and at the other station in a loudspeaker, means at each station for dividing the frequency band of speech signals impressed on the transmitter thereat into two subbands, and means at each station selectively responsive to the frequencies of one subband for connecting the corresponding transmitter toone of said lines and for simultaneously disabling the loudspeaker.

3. In a loudspeaking intercommunicating system, a first station, a second station, a line extending between said stations, a transmitter at said first station, a loudspeaker at said second station, means at said first station for dividing the frequency band of speech signals impressed on the transmitter thereat into two subbands, and means selectively responsive to frequencies of one subband for interconnecting the transmitter of said first station and the loudspeaker of said second station by way of said line. v 4. In a loudspeaking intercommunicating system, a first station, a second station, a line extending between said stations, a transmitter at said first station, a loudspeaker at said second station, and switching means responsive to the activation of said transmitter by signals in the speech frequency band for connecting said transmitter to said loudspeaker by way of said line and for eliminating certain frequencies of the speech band from said line.

5. In a loudspeaking intercommunicating system, a first station, a second station, a line ex- ,tending between said stations, a transmitter at said first station, a loudspeaker at said second station, and switching means responsive to the activation of the transmitter at said first station by signals in the speech frequency band for connecting said transmitter to the loudspeaker at said second station by way of said line and for transmitting over said line only certain frequencies of the speech band.

6. In a loudspeaking intercommunicating system. a first station, a second station, a line ex.-

7. A loudspeaking intercommunicating system in accordance with claim 6 in which the responsive means comprises a relay connected to the terminals of the capacity element.

BFIn a loudspeaking intercommunicating system, a first station, a second station, a line extending between said stations, a transmitter at said first station, a signal at said second station, and electromagnetically operated means responsive to the activation of the transmitter at said first station by speech signals for completing a connection between said stations by way of said line and for simultaneously actuating the signal at said second station. 5

9. In a loudspeaking intercommunicating system, a first station, a transmitter thereat, a second station, a signal thereat, a line extending between said stations, and means including electromagnetically controlled switching means responsive to certain frequencies of the speech band generated by the transmitter at' said first station for completing a connection between said stations by way of said line and for actuating the signal at said second station.

10. In a loudspeaking intercommunicating system, a first station having a speech transmitting device, a second station, a normally discontinuous line extending between said stations, means at said first station responsive to speech signals impressed on the transmitting device thereat for selecting a band of frequencies comprising frequencies below 400 cycles, and means responsive to .the selected band of frequencies for projecting the remaining frequencies of the speech band over said line. I

11. The method of transmitting speech intelligence over a line between two stations which comprises generating atone station signals which include all frequencies of the speech band, subdividing the speech band of frequencies into two subbands including respectively, those frequencies not essential to good speech articulation and those frequencies which are essential to good articulation, and projecting only those frequencies which are essential to good articulation over said line.

PAUL E. DEMERS.

REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES PATEN'rs Number 1 Herrick May 12, 1942 

